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African Journal of Environmental Science and Technology Vol. 6(10), pp. 403-408, October 2012Available online at http://www.academicjournals.org/AJESTDOI: 10.5897 / AJEST12.124ISSN 1996-0786 ©2012 Academic Journals

Full Length Research Paper Determination of selected heavy metals in inland fresh

water of lower River Niger drainage inNorth Central Nigeria

Olatunde Stephen Olatunji1* and Oladele Osibanjo2

1Department of Chemistry, Faculty of Applied Sciences, Cape Peninsula University of Technology

Bellville, Western Cape, South Africa.2Department of Chemistry, Faculty of Science, University of Ibadan, Ibadan, Oyo State Nigeria.

Accepted 23 August, 2012

The concentrations of some ferruginous ore associated heavy metals were determined in freshwaterfrom River Niger. Water samples were collected from both upstream and downstream along themainstream drainage channel, traversing past the steel production industry Ajaokuta between 2003 and2005. The water samples were digested according to standard methods and tested for Cadmium (Cd),Manganese (Mn), Chromium (Cr), Nickel (Ni), Cupper (Cu), Zinc (Zn) and Lead (Pb) using Unicam 969atomic absorption spectrophotometer. The mean concentrations (mg/L) of heavy metals were: Mn, 3.85± 0.93; Zn, 2.72 ± 0.57; Cu, 2.17 ± 0.73; Cr, 2.08 ± 1.27; Ni, 0.78 ± 0.12; Cd, 0.05 ± 0.02; Pb, 0.03 ± 0.02. Theconcentration of Mn, 1.74 to 8.37 mg/L; Cu, 0.58 to 4.50 mg/L; Cd, 0.02 to 0.13 mg/L were variable andinundating. The variations in heavy metal levels between sampling stations were not significant (P >0.05) with relative standard deviation from 2% for Cd and Pb to 12.7% for Cr. The order of dispersion (2to 14%) showed that the measured metals are nearly homogenously distributed in the water with Cr,

Mn, Cu and Zn having the highest concentration variations in the water samples. The concentrations ofthe evaluated heavy metals were within the guideline levels for freshwaters, and did not appear to havesignificant negative impact on the water quality.

Key words: Heavy metals, freshwater, concentrations, quality, variation, distribution.

INTRODUCTION

Water quality is fundamental to the health andsustenance of aquatic ecosystems and hydrology. Thebenefits of renewable freshwater to humans includewater for drinking, irrigation, industrial uses, production offish, and for such in-stream uses as recreation,transportation and waste disposal (Jackson et al., 2001).Water also plays a major role in the cycling of materialsand can be a vector if it becomes a source that spreadharmful substances and diseases.

The quality and stability of river water depends on suchfactors as lithology of catchment, climatic conditions,

*Corresponding author. E-mail: [email protected]. Tel:+27822912934.

atmospheric and anthropogenic inputs etc (Berner andBerner, 1987; Bricker and Jones, 1995; Markich andBrown, 1998; Bellos et al., 2004). Water can be stressedwith heavy metal load sourced from weatheredsoils/rocks, mining and metallurgical releases andindustrial emissions (Boari et al., 1997; Adams, 2001)This may exert unsustainable demand on freshwater byaquatic microflora/microfauna, aquatic wild and humanswho depend on such waters, and may be exposed tocontamination by heavy metals (Biney et al., 1994Edorh, 2007) and other contaminants and theideleterious consequences. Although heavy metals do notremain in water for long, water catchments can become asource of concern if the levels of heavy metals in themexceed health guideline concentration criteria (Salomonand Forstner, 1984).

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404 Afr. J. Environ. Sci. Technol.

The protection of water and aquatic ecosystem fromadverse effects of pollutants such as heavy metals iscentral to environmental risk management (Bere andTundisi, 2011). Evaluation and understanding thesources and impact relationship of the effects of heavymetals in water bodies and biological species is important

for effective water management, and the preservation ofthe aquatic ecosystem. This is because trace amounts ofsuch metals can accumulate in the food chain, eventuallycausing diseases (Gulson et al., 1996; ATSDR, 1999;Windham, 2000). The assessment of water quality istherefore a vital tool to manage land and water resourceswithin a particular catchment (Petts and Calow, 1996).

The levels of heavy metals in some inland rivers in thehinterland and Niger Delta, especially those which emptytheir content into coastal waters have been reported(Mombeshora et al., 1981; Ajayi and Osibanjo, 1981;Ndiokwere and Guin, 1983; Wogu and Okaka, 2011).Amoo et al. (2005) and Oyewale and Musa (2006)reported levels of heavy metals in Lakes Kainji and Jebbaon the upper reach of River Niger. However,environmental and health data concerning the levels andprevalence of heavy metals in inland water of lower RiverNiger drain are scarce and scattered. There is need for arational and systematic assessment of heavy metals inthe river system environment in view of the siting of ametallurgical industry along the bank of River Niger atAjaokuta.

In this study, the concentration of Cadmium (Cd), Lead(Pb), Cupper (Cu), Nickel (Ni), Zinc (Zn), Manganese(Mn) and Chromium (Cr) were determined in watersamples collected from River Niger at Ajaokuta, in orderto establish their baseline levels.

MATERIALS AND METHODS

Study area

River Niger arises from Fouta Djallon highland arriving in Nigeriathrough Kebbi State and flows through to the Atlantic Ocean. Thestudy location is within the extends of River Niger stretch traversingAjaokuta area in the lower River Niger regime, which is geo-referenced within the Lokoja – Okene area delimited by latitudes 7°and 8°N and longitudes 6°and 7°E. Lower River Niger is drained bythe Niger-Benue River system, which stretches beyond Lokojadown to the Niger Delta where it empties its content into the AtlanticOcean. Contribution from watershed tributary streams and rivers tothe east and west flowing north-south is significant (Figure 1).

However, the hydrologies of discharges from the tributaries aregrossly changeable and inundating during rainy season to almostcompletely dry cut in the course of the dry season (GSN, 1986).Activities on lower River Niger around Ajaokuta include fishing,transportation and domestic uses by communities along the bank ofthe river. A power station and steel production company seatsalong the bank of River Niger at Geregu and Ajaokuta, respectively.

Sample collection

Sampling was carried out along the mainstream drainage channelof River Niger traversing past Ajaokuta Steel Company Complex,located on N 07°30, 669”, E 006°42, 275” and altitude range 74 to

120 m at Ajaokuta, North Central Nigeria as shown in Figure 1Water samples were randomly collected upstream (N 07°32,745"E 006° 42,712") and downstream (N 07° 28,678", E 0060 42,492"River Niger off Ajaokuta Steel Company over a period of 24months, encompassing the dry and wet seasons betweenDecember, 2003 and November, 2005.

A total of 80 water samples were collected in nitric acid pre-treated 1.5 L polypropylene bottles for metal detection and in 500ml amber coloured bottles for physico-chemical assessment. Thebottles were labelled and stored in a cooler for onward transfer tothe laboratory.

Sample preparation and the determination of physico-chemicacharacteristic

The water samples were processed according to the methodprescribed by the American Public Health Association (APHA1998). The pH and electrical conductivity (EC) of the water sampleswere tested using pre-calibrated pH and conductivity meter, whilethe determination of dissolved oxygen (DO), biochemical oxygendemand (BOD), chemical oxygen demand (COD), nitrate (NO3

-)phosphate (PO4

3-) and ammonia (NH4

+) were tested using the

methods of the APHA (1998).

Determination of heavy metals

Heavy metals in the water samples were determined as describedby APHA (1998). The digested water samples were quantified fothe heavy metals Cd, Cr, Mn, Ni, Cu, Zn and Pb in flame of Unicam969 atomic absorption spectrometer (FAAS). Procedural blankswere prepared and aspirated along with the analytical samples inorder to correct for background absorption. The availability anddistribution of heavy metals in River Niger water was evaluated bycomparing the statistical mean levels of the metals in the watersamples, relative to each other.

Determination of seasonal variability of metals

Seasonal differences in variability of metal levels was determinedby comparing the concentration levels of the heavy metals detectedin the water samples during wet season with levels detected duringdry season using one way analysis of variance (ANOVA).

Recovery studies

The test of reliability on heavy metals concentration data werechecked against spiked water sample in recovery studies carriedout in replicates to validate the digestion method. The recovery andcoefficient of variation (CV) of the metals in replicates of the spikeswater samples ranged: Cd, 91.42 to 93.35%, CV 3.35 to 4.65%Mn, 89.46 to 92.84%, CV 4.52 to 6.20; Cr, 87. 65 to 90.29%, CV4.25 to 9.41%; Ni, 91.55 to 94.45%, CV 5.28 to 10.24%; Cu, 92.48to 94.07%, CV 6.31 to 10.68%; Zn, 91.36 to 93.94%, CV 7.50 to14.15%; Pb, 92.26 to 95.15%, CV 3.82 to 5.75%. The erroassociated with the determination of the concentration of the heavymetals Cd, Mn, Cr, Ni, Cu, Zn and Pb in River Niger water wereconsidered negligible.

RESULTS

Physico-chemical characteristics of water samples

The result of the determination of physico-chemica

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Olatunji and Osibanjo 405

Figure 1. Lower River Niger drainage system with surrogate watershed hydrological pattern on the Lokoja survey area, NorthCentral Nigeria (GSN, 1986).

properties of River Niger water collected at differentsampling stations upstream and downstream AjaokutaSteel Company at Ajaokuta are shown in Table 1.

The pH of the river water measured at differentsampling station ranged from 6.9 to 7.2 (7.00 ± 0.12).Water temperature ranged between 24 to 28°C (26.17 ±1.47°C), with the least temperature measured during wetseason. EC of the water ranged from 0.85 to 2.34 µS cm

-

1 (1.74 ± 0.50 µS cm

-1), and correlates (γ = 0.58 – 0.71)

with total dissolved solid (TDS) levels which ranged from19.8 to 77.54 mg/L (42.95 ± 20.61 mg/L). DOconcentrations ranged from 5.40 to 7.85 mg/L (6.67 ±

0.91 mg/L), while oxygen demand requirements wereBOD, 4.27 to 9.62 mg/L (5.58 ± 2.07 mg/L), and COD18.52 to 22.46 mg/L (19.56 ± 1.47 mg/L). Nutrient loadlevels were NO3

-, 0.65 to 1.49 mg/L (1.03 ± 0.30 mg/L)

PO43-

, 0.41 to 0.87 mg/L (0.63 ± 0.15 mg/L) and NH4+

0.15 to 0.42 mg/L (0.32 ± 0.09 mg/L).

Concentration levels, distribution and seasonavariation of heavy metals

The seasonal concentrations (mg/L) range of heavy

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DISCUSSION

The water samples are sufficiently neutral meeting bothdrinking and freshwater quality requirement 6.5 to 8.5.DO levels and oxygen demand requirements (BOD, werewithin guideline values for fresh water, except in two

water pools (2/80) by the riverside with high domesticactivities with DO of < 6.00 mg/L, that is, 5.40 and 5.85mg/L. The European Union (EU, 2006) freshwaterfisheries directive requires that when oxygenconcentration falls below 6.00 mg/L, members stateshould implement provision of article 7(3), which pursuesan agenda for water renewal, and aquatic life‘conservation and sustainability. These levels are not athreat to the health of the river water since nutrient loadNO3

-, 0.65 to 1.49 mg/L, PO4

3-, 0.41 to 0.87 mg/L and

NH4+, 0.15 to 0.42 mg/L are low. The low nutrient load

also explains the low to moderate levels of BOD andCOD requirement. The levels of DO, BOD and CODobserved are consistent with the findings of Tripathi et al.(1999), and were within guideline levels. Nutrient levelswere also within the Canadian Council of the Ministers ofEnvironment (CCME) guideline levels in freshwater (NO3

-

, (13 mg/L); PO43-

, (0.1 mg/L) and NH4+, (0.025 and 1.0

mg/L for non-ionized ammonia and total ammonium,respectively). Analysis of variance showed thattemperature; pH, DO and conductivity of water did notshow significant variation (p > 0.05) between samplingstations. This suggests that the water quality is adequatefor supporting aquatic life.

The concentrations of the measured heavy metals inthe water samples varied with seasons. The variations inconcentration of Cd (±0.01 to ±0.02) and Pb (±0.01 to

±0.03) in the pooled water samples and betweensampling stations were not significant (p > 0.05), withrelative standard deviations of 2%, Cd and Pb to 12.7%Cr, which indicate uniform distribution as confirmed bythe low values (2 to 14%) of order of dispersion.

River Niger water at Ajaokuta did not contain excessivelevels of heavy metals when compared to results fromother studies. This finding is consistent with those ofAmoo et al. (2005) in freshwater from Lake Kainji on theupper reach of River Niger. Kakulu and Osibanjo (1992)reported higher concentrations of Cd, Pb, Ni, Cu and Znin water collected from Warri River, and higher Cd, Pb,Cu, and Zn levels in waters from Calabar River, than

recorded in this study. It has been reported that thedifferences in geography and geologies, as well asactivities in various rivers affects the amount of metalspresent (Berner and Berner, 1987; Bricker and Jones,1995).

The concentration levels of the measured heavy metalsin River Niger water may partly be a function of theprevailing pH and seasonal variations. According toOgunfowokan et al. (2005), the availability and toxicity ofchemical species of many heavy metals in their aquaticenvironment is altered depending on the pH of waterbody.

Olatunji and Osibanjo 407

The level of Mn was noted to be the most abundant inrespect of the other metals determined during the studyfollowed by Zn. Cd had the least concentration amongthe metals determined in water samples from River Nigeat Ajaokuta. Availability of the metals in River Niger is inthe order Mn > Zn > Cu > Cr > Ni > Cd > Pb. The

availability sequence observed in this study compareswith the report of El-Rayis and Saad (1985) for dissolvedmetals in surface and subsurface water along the Rosettabranch on River Nile to the eastern Mediterranean. Theavailability of heavy metals in the upstream drainage areaof River Niger is however not significantly (p > 0.05)different from the downstream drainage area, thoughmetals abundance trend is the same.

The high concentration of heavy metals in the watersamples during the dry seasons under the study period isdue to the fact that water levels decrease in rivers, resultsin increase in concentration of the metals. As a result, theconcentrations of the measured metals were higherduring dry season than in wet season, exept for Pb andCd which were only slightly altered.

Water quality can be affected when the rate oatmospheric deposition, storm water run offs, domestic oindustrial waste water discharges, surpasses the carriagecapacity of water (US EPA, 1998). The buffering, dilutionand self-purification capacity of large water bodies tendsto leave heavy metals levels and those of othehydrophilic substances low (Ajayi and Osibanjo, 1981). Iwas reported that among water and aquatic qualityparameters, salinity, pH and temperature bears direcstress effect that are naturally and seasonally variablewithin ecosystem types and for which natural biologicacommunities are adapted to the site-specific conditions

(ANZECC, 2000). Water salinity, pH and temperaturehave major effect on the bioavailable concentrations omost heavy metals. Thus, the threshold levels for salinitypH, temperature and priority heavy metals may need tobe based on site-specific eco-toxicology and biologicaeffects data.

Conclusion

The concentrations of heavy metals in River Niger watersat Ajaokuta were found to be low and within guidelinelevels recommended for freshwater. Results of this study

can serve as baseline environmental data benchmark formonitoring build-up of heavy metals in streams and riversaround the metallurgical and steel productionenvironment.

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